Sea Floor Spreading

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Vocabulary

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Mid-ocean ridge: The longest chain of mountains in the world, mostly underwater.
Sonar: Sound waves that bounce off objects so scientists can tell whats at the bottom of the ocean.
Sea-floor spreading: Harry Hess's theory that at the mid-ocean ridge, molten material rises from the mantle and erupts. The molten material then spreads out, pushing older rock to both sides of the ridge.
Deep-ocean trenches: A deep-ocean trench forms where the oceanic crust bends downward.
Subduction: The process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle.

Outline

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Sea-floor Spreading:

• Molten Material erupts
• creates new rock
• puses old rock back into trench into mantle

Evidence from Molten Material:

• Rocks at bottom of the ocean look like pillows just like when lava cools
  • examined with submersible called Alvin

Evidence from Magnetic stripes:

• Ocean floor has a pattern of stripes that are magnetic
  • Magma has iron so when the magma comes out the iron lands on the rock
    • called magnetic memory

Evidence from Drilling Samples:

• The rocks on the ocean floor gave these results
  • Rocks farther from the mid-ocean ridge were older
  • The closer the rocks were to the mid-ocean ridge the newer they were

Subduction and the earths oceans:

• Subduction is when old rock goes into a trench and back in the mantle when sea floor spreading occurs.
  • Pacific ocean is getting smaller because the trench is too big
  • Atlantic ocean is getting bigger because the trench is too small.

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